docs: def update_sources(self):
          """Update local sources based on response from Elasticsearch"""
          ES_documents = self.get_docs_sources_from_ES()
  
          for doc, update_spec, action_buffer_index, get_from_ES in self.doc_to_update:
              if get_from_ES:
                  # Update source based on response from ES
                  ES_doc = next(ES_documents)
                  if ES_doc["found"]:
                      source = ES_doc["_source"]
                  else:
                      # Document not found in elasticsearch,
                      # Seems like something went wrong during replication
                      LOG.error(
                          "mGET: Document id: %s has not been found "
                          "in Elasticsearch. Due to that "
                          "following update failed: %s",
                          doc["_id"],
                          update_spec,
                      )
                      self.reset_action(action_buffer_index)
                      continue
              else:
                  # Get source stored locally before applying update
                  # as it is up-to-date
                  source = self.get_from_sources(doc["_index"], doc["_type"], doc["_id"])
                  if not source:
                      LOG.error(
                          "mGET: Document id: %s has not been found "
                          "in local sources. Due to that following "
                          "update failed: %s",
                          doc["_id"],
                          update_spec,
                      )
                      self.reset_action(action_buffer_index)
                      continue
  
              updated = self.docman.apply_update(source, update_spec)
  
              # Remove _id field from source
              if "_id" in updated:
                  del updated["_id"]
  
              # Everytime update locally stored sources to keep them up-to-date
              self.add_to_sources(doc, updated)
  
              self.action_buffer[action_buffer_index][
                  "_source"
              ] = self.docman._formatter.format_document(updated)
  
          # Remove empty actions if there were errors
          self.action_buffer = [
              each_action for each_action in self.action_buffer if each_action
          ]